1. Field of the Invention
The present invention relates to an apparatus and method for receiving a transmission in a mobile communication system. More particularly, the present invention relates to an apparatus and a method for reducing power consumption of a receiver by performing a Hybrid Automatic Repeat reQuest (HARQ) according to a detected decoding error.
2. Description of the Related Art
With advances in technology, mobile communication systems now include wireless data packet communication systems of high speed and high quality. Such communication systems provide data service and multimedia service, beyond the initial voice-oriented services. The development of High Speed Downlink Packet Access (HSDPA), which progressed as part of the 3rd Generation Partnership Project (3GPP), can be viewed as a representative effort for providing a wireless data packet transport service having high quality at over 2 Mbps in the 3G mobile communication system.
In a data packet communication system, when a transport block to be coded exceeds a certain bit size, the mobile communication system performs a code block segmentation. The code block segmentation segments the transport block into a plurality of code blocks, each code block having a size smaller than the certain bit size.
FIG. 1 depicts a conventional channel coding process in a mobile communication system.
Referring to FIG. 1, a transport block 100 includes a Cyclic Redundancy Code (CRC) 110 for detecting an error in the transport block. The CRC 110 goes through the code block segmentation 120 along with the transport block 100. The code block segmentation 120 segments the single transport block 100, including the CRC 110, into a smaller size according to a preset rule and generates a plurality of code blocks.
The segmented code blocks pass through the channel coding 130 (e.g. turbo coding) independently. The coded code blocks are then reconstituted to produce one bit stream through a code block concatenation 140. Typically, the generated bit stream is transmitted using a rate matching (e.g. bitwise puncture or bitwise repetition) and a channel interleaving.
In the mobile communication system, if the transmission contains errors, the data is retransmitted. Typically, the retransmission is carried out using a Hybrid Automatic Repeat reQuest (HARQ) process. In the HARQ process, a receiver sends a Negative ACKnowledgment (NACK) signal to a transmitter in a backward channel when the received transport block 100 is corrupted. When the response of the receiver for the transmitted transport block 100 is the NACK, the HARQ transmitter performs the retransmission. The HARQ transmission differs from the general ARQ transmission in that its performance can be enhanced using a soft combination (e.g. chase combining or incremental redundancy) of the previously received coded values, which are stored in the receiver, and the currently received coded values in the coded code blocks.
FIG. 2 depicts a conventional HARQ process in a mobile communication system.
In the conventional HARQ process, the receiver decodes a signal received via a receive antenna, checks for error using the CRC and conducts the retransmission.
In more detail, the receiver segments one received transport block, including the CRC, into a plurality of code blocks having a size according to a preset rule.
Next, the receiver independently codes (e.g. turbo coding) the segmented code blocks and generates one bit stream using the code block concatenation on the coded code blocks. Typically, the generated bit stream is transmitted after passing through rating matching (e.g. bitwise puncture or bitwise repetition) and channel interleaving.
When the decoding error occurs, the receiver performs the retransmission using HARQ. In the HARQ process, the receiver decodes every code block in the retransmission. However, not all code blocks are subject to corruption. That is, the decoding is conducted unnecessarily on not only the corrupted code blocks but also the normally decoded code blocks that do not contain an error in their retransmission. As a result, the power consumption of the receiver is unnecessarily increased.